diff --git a/Nerd_STF/Mathematics/Abstract/IPolygon.cs b/Nerd_STF/Mathematics/Abstract/IPolygon.cs
index 4131aa3..038f0b0 100644
--- a/Nerd_STF/Mathematics/Abstract/IPolygon.cs
+++ b/Nerd_STF/Mathematics/Abstract/IPolygon.cs
@@ -10,6 +10,7 @@ public interface IPolygon<T> : IAverage<T>, IEquatable<T>,
     public float Perimeter { get; }
 
     public Float3[] GetAllVerts();
+    public Line[] GetOutlines();
     
     public static abstract T operator +(T poly, Float3 offset);
     public static abstract T operator -(T poly, Float3 offset);
diff --git a/Nerd_STF/Mathematics/Geometry/Quadrilateral.cs b/Nerd_STF/Mathematics/Geometry/Quadrilateral.cs
new file mode 100644
index 0000000..f1c07c7
--- /dev/null
+++ b/Nerd_STF/Mathematics/Geometry/Quadrilateral.cs
@@ -0,0 +1,436 @@
+namespace Nerd_STF.Mathematics.Geometry;
+
+public class Quadrilateral : IClosestTo<Float3>, IContains<Float3>, IContainsPartial<Line>,
+    IFromTuple<Quadrilateral, (Float3 a, Float3 b, Float3 c, Float3 d)>, IPolygon<Quadrilateral>,
+    ISplittable<Quadrilateral, (Float3[] As, Float3[] Bs, Float3[] Cs, Float3[] Ds)>,
+    ISubdivide<Quadrilateral[]>, ITriangulate, IWithinRange<Float3, float>
+{
+    public float Area
+    {
+        get // Modification of Heron's Formula to work with quadrilaterals.
+        {
+            float a = AB.Length, b = BC.Length, c = CD.Length, d = DA.Length,
+                  s = (a + b + c + d) / 2;
+
+            Angle theta1 = Angle.FromPoints(this.a, this.b, this.c),
+                  theta2 = Angle.FromPoints(this.c, this.d, this.a);
+
+            float cos = Mathf.Cos((theta1 + theta2) / 2);
+
+            return Mathf.Sqrt((s - a) * (s - b) * (s - c) * (s - d) - (a * b * c * d * cos * cos));
+        }
+    }
+    public Float3 Midpoint => Float3.Average(a, b, c, d);
+    public float Perimeter => AB.Length + BC.Length + CD.Length + DA.Length;
+
+    public Line AB
+    {
+        get => (a, b);
+        set
+        {
+            a = value.a;
+            b = value.b;
+        }
+    }
+    public Line AC
+    {
+        get => (a, c);
+        set
+        {
+            a = value.a;
+            c = value.b;
+        }
+    }
+    public Line BC
+    {
+        get => (b, c);
+        set
+        {
+            b = value.a;
+            c = value.b;
+        }
+    }
+    public Line BD
+    {
+        get => (b, d);
+        set
+        {
+            b = value.a;
+            d = value.b;
+        }
+    }
+    public Line CD
+    {
+        get => (c, d);
+        set
+        {
+            c = value.a;
+            d = value.b;
+        }
+    }
+    public Line DA
+    {
+        get => (d, a);
+        set
+        {
+            d = value.a;
+            a = value.b;
+        }
+    }
+
+    public Triangle ABC
+    {
+        get => (a, b, c);
+        set
+        {
+            a = value.a;
+            b = value.b;
+            c = value.c;
+        }
+    }
+    public Triangle BCD
+    {
+        get => (b, c, d);
+        set
+        {
+            b = value.a;
+            c = value.b;
+            d = value.c;
+        }
+    }
+    public Triangle CDA
+    {
+        get => (c, d, a);
+        set
+        {
+            c = value.a;
+            d = value.b;
+            a = value.c;
+        }
+    }
+    public Triangle DAB
+    {
+        get => (d, a, b);
+        set
+        {
+            d = value.a;
+            a = value.b;
+            b = value.c;
+        }
+    }
+
+    public Angle AngleABC => Angle.FromPoints(a, b, c);
+    public Angle AngleBCD => Angle.FromPoints(b, c, d);
+    public Angle AngleCDA => Angle.FromPoints(c, d, a);
+    public Angle AngleDAB => Angle.FromPoints(d, a, b);
+
+    public Float3 a, b, c, d;
+
+    public Quadrilateral() : this(Float3.Zero, Float3.Zero, Float3.Zero, Float3.Zero) { }
+    public Quadrilateral(Float3 a, Float3 b, Float3 c, Float3 d)
+    {
+        this.a = a;
+        this.b = b;
+        this.c = c;
+        this.d = d;
+    }
+    public Quadrilateral(Line ab, Line bc, Line cd, Line da)
+    {
+        if (ab.b != bc.a || bc.b != cd.a || cd.b != da.a || da.b != ab.a)
+            throw new DisconnectedLinesException(ab, bc, cd, da);
+
+        a = ab.a;
+        b = bc.a;
+        c = cd.a;
+        d = da.a;
+    }
+    public Quadrilateral(float x1, float y1, float x2, float y2, float x3, float y3,
+        float x4, float y4)
+    {
+        a = (x1, y1, 0);
+        b = (x2, y2, 0);
+        c = (x3, y3, 0);
+        d = (x4, y4, 0);
+    }
+    public Quadrilateral(float x1, float y1, float z1, float x2, float y2, float z2,
+        float x3, float y3, float z3, float x4, float y4, float z4)
+    {
+        a = (x1, y1, z1);
+        b = (x2, y2, z3);
+        c = (x3, y3, z3);
+        d = (x4, y4, z4);
+    }
+    public Quadrilateral(Fill<Float3> fill) : this(fill(0), fill(1), fill(2), fill(3)) { }
+    public Quadrilateral(Fill<Int3> fill) : this(fill(0), fill(1), fill(2), fill(3)) { }
+    public Quadrilateral(Fill<Line> fill) : this(fill(0), fill(1), fill(2), fill(3)) { }
+    public Quadrilateral(Fill<float> fill) : this(fill(0), fill(1), fill(2), fill(3),
+        fill(4), fill(5), fill(6), fill(7), fill(8), fill(9), fill(10), fill(11)) { }
+    public Quadrilateral(Fill<int> fill) : this(fill(0), fill(1), fill(2), fill(3),
+        fill(4), fill(5), fill(6), fill(7), fill(8), fill(9), fill(10), fill(11)) { }
+
+    public Float3 this[int index]
+    {
+        get => index switch
+        {
+            0 => a,
+            1 => b,
+            2 => c,
+            3 => d,
+            _ => throw new IndexOutOfRangeException(nameof(index))
+        };
+        set
+        {
+            switch (index)
+            {
+                case 0:
+                    a = value;
+                    break;
+
+                case 1:
+                    b = value;
+                    break;
+
+                case 2:
+                    c = value;
+                    break;
+
+                case 3:
+                    d = value;
+                    break;
+
+                default: throw new IndexOutOfRangeException(nameof(index));
+            }
+        }
+    }
+
+    public Float3 this[Index index]
+    {
+        get => this[index.IsFromEnd ? 4 - index.Value : index.Value];
+        set => this[index.IsFromEnd ? 4 - index.Value : index.Value] = value;
+    }
+    public Float3[] this[Range range]
+    {
+        get
+        {
+            int start = range.Start.IsFromEnd ? 4 - range.Start.Value : range.Start.Value;
+            int end = range.End.IsFromEnd ? 4 - range.End.Value : range.End.Value;
+            List<Float3> res = new();
+            for (int i = start; i < end; i++) res.Add(this[i]);
+            return res.ToArray();
+        }
+        set
+        {
+            int start = range.Start.IsFromEnd ? 4 - range.Start.Value : range.Start.Value;
+            int end = range.End.IsFromEnd ? 4 - range.End.Value : range.End.Value;
+            for (int i = start; i < end; i++) this[i] = value[i];
+        }
+    }
+
+    public static Quadrilateral Average(params Quadrilateral[] vals)
+    {
+        (Float3[] As, Float3[] Bs, Float3[] Cs, Float3[] Ds) = SplitArray(vals);
+        return (Float3.Average(As), Float3.Average(Bs), Float3.Average(Cs), Float3.Average(Ds));
+    }
+    public static Quadrilateral Lerp(Quadrilateral a, Quadrilateral b, float t,
+        bool clamp = true) => (Float3.Lerp(a.a, b.a, t, clamp), Float3.Lerp(a.b, b.b, t, clamp),
+                               Float3.Lerp(a.c, b.c, t, clamp), Float3.Lerp(a.d, b.d, t, clamp));
+    public static (Float3[] As, Float3[] Bs, Float3[] Cs, Float3[] Ds) SplitArray(
+        params Quadrilateral[] vals)
+    {
+        Float3[] As = new Float3[vals.Length],
+                 Bs = new Float3[vals.Length],
+                 Cs = new Float3[vals.Length],
+                 Ds = new Float3[vals.Length];
+        for (int i = 0; i < vals.Length; i++)
+        {
+            As[i] = vals[i].a;
+            Bs[i] = vals[i].b;
+            Cs[i] = vals[i].c;
+            Ds[i] = vals[i].d;
+        }
+        return (As, Bs, Cs, Ds);
+    }
+
+    public static float[] ToFloatArrayAll(params Quadrilateral[] vals)
+    {
+        float[] result = new float[12 * vals.Length];
+        for (int i = 0; i < vals.Length; i++)
+        {
+            int p = i * 12;
+            result[p +  0] = vals[i].a.x;
+            result[p +  1] = vals[i].a.y;
+            result[p +  2] = vals[i].a.z;
+            result[p +  3] = vals[i].b.x;
+            result[p +  4] = vals[i].b.y;
+            result[p +  5] = vals[i].b.z;
+            result[p +  6] = vals[i].c.x;
+            result[p +  7] = vals[i].c.y;
+            result[p +  8] = vals[i].c.z;
+            result[p +  9] = vals[i].d.x;
+            result[p + 10] = vals[i].d.y;
+            result[p + 11] = vals[i].d.y;
+        }
+        return result;
+    }
+
+    public Float3 ClosestTo(Float3 point)
+    {
+        Float3 abClosest = AB.ClosestTo(point),
+               bcClosest = BC.ClosestTo(point),
+               cdClosest = CD.ClosestTo(point),
+               daClosest = DA.ClosestTo(point);
+
+        // Very inefficient way to select the closest point.
+
+        float abDist = (abClosest - point).Magnitude,
+              bcDist = (bcClosest - point).Magnitude,
+              cdDist = (cdClosest - point).Magnitude,
+              daDist = (daClosest - point).Magnitude;
+
+        float min = Mathf.Min(abDist, bcDist, cdDist, daDist);
+        if (min == abDist) return abClosest;
+        else if (min == bcDist) return bcClosest;
+        else if (min == cdDist) return cdClosest;
+        else return daClosest;
+    }
+
+    public bool Equals(Quadrilateral? other) => other is not null &&
+        a == other.a && b == other.b && c == other.c && d == other.d;
+    public override bool Equals(object? obj)
+    {
+        if (obj is null) return false;
+        else if (obj is Quadrilateral quad) return Equals(quad);
+        return false;
+    }
+    public override int GetHashCode() => base.GetHashCode();
+    public override string ToString() => $"{nameof(Quadrilateral)} {{ a: {a}, b: {b}, c: {c}, d: {d} }}";
+
+    public bool Contains(Float3 point) => Contains(point, 0.05f);
+    public bool Contains(Float3 point, float tolerance)
+    {
+        Triangle pab = (point, a, b),
+                 pbc = (point, b, c),
+                 pcd = (point, c, d),
+                 pda = (point, d, a);
+        return Mathf.Absolute(Area - (pab.Area + pbc.Area + pcd.Area + pda.Area)) < tolerance;
+    }
+    public bool Contains(Line line) => Contains(line, 0.05f);
+    public bool Contains(Line line, float tolerance, float step = Calculus.DefaultStep)
+    {
+        for (float t = 0; t <= 1; t += step)
+            if (!Contains(Float3.Lerp(line.a, line.b, t), tolerance)) return false;
+        return true;
+    }
+
+    public bool ContainsPartially(Line line) => ContainsPartially(line, 0.05f);
+    public bool ContainsPartially(Line line, float tolerance, float step = Calculus.DefaultStep)
+    {
+        for (float t = 0; t <= 1; t += step)
+            if (Contains(Float3.Lerp(line.a, line.b, t), tolerance))
+                return true;
+        return false;
+    }
+
+    public Float3[] GetAllVerts() => new[] { a, b, c, d };
+    public Line[] GetOutlines() => new[] { AB, BC, CD, DA };
+
+    public Quadrilateral[] Subdivide()
+    {
+        Float3 abMid = AB.Midpoint,
+               bcMid = BC.Midpoint,
+               cdMid = CD.Midpoint,
+               daMid = DA.Midpoint,
+               abcdMid = Midpoint;
+
+        return new Quadrilateral[4]
+        {
+            (a, abMid, abcdMid, daMid),
+            (b, bcMid, abcdMid, abMid),
+            (c, cdMid, abcdMid, bcMid),
+            (d, daMid, abcdMid, cdMid)
+        };
+    }
+    public Quadrilateral[] Subdivide(int iterations)
+    {
+        Quadrilateral[] active = new[] { this };
+        for (int i = 0; i < iterations; i++)
+        {
+            List<Quadrilateral> newQuads = new();
+            foreach (Quadrilateral quad in active) newQuads.AddRange(quad.Subdivide());
+            active = newQuads.ToArray();
+        }
+        return active;
+    }
+
+    public Triangle[] Triangulate()
+    {
+        if (AC.Length > BD.Length) return new Triangle[]
+        {
+            (a, b, c),
+            (c, d, a)
+        };
+        else return new Triangle[]
+        {
+            (b, c, d),
+            (d, a, b)
+        };
+    }
+
+    public bool WithinRange(Float3 point, float range) =>
+        WithinRange(point, range, Calculus.DefaultStep);
+    public bool WithinRange(Float3 point, float range, float step)
+    {
+        // Just like line, this is probably optimizable but who cares?
+        return AB.WithinRange(point, range, step) ||
+               BC.WithinRange(point, range, step) ||
+               CD.WithinRange(point, range, step) ||
+               DA.WithinRange(point, range, step);
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+    public IEnumerator<Float3> GetEnumerator()
+    {
+        yield return a;
+        yield return b;
+        yield return c;
+        yield return d;
+    }
+
+    public Float3[] ToArray() => new[] { a, b, c, d };
+    public Fill<Float3> ToFill()
+    {
+        Quadrilateral @this = this;
+        return i => @this[i];
+    }
+    public List<Float3> ToList() => new() { a, b, c, d };
+
+    public float[] ToFloatArray() => new[] { a.x, a.y, a.z,
+                                             b.x, b.y, b.z,
+                                             c.x, c.y, c.z,
+                                             d.x, d.y, d.z };
+
+    public static Quadrilateral operator +(Quadrilateral q, Float3 offset) =>
+        new(q.a + offset, q.b + offset, q.c + offset, q.d + offset);
+    public static Quadrilateral operator -(Quadrilateral q, Float3 offset) =>
+        new(q.a - offset, q.b - offset, q.c - offset, q.d - offset);
+    public static Quadrilateral operator *(Quadrilateral q, float factor) =>
+        new(q.a * factor, q.b * factor, q.c * factor, q.d * factor);
+    public static Quadrilateral operator *(Quadrilateral q, Float3 factor) =>
+        new(q.a * factor, q.b * factor, q.c * factor, q.d * factor);
+    public static Quadrilateral operator /(Quadrilateral q, float factor) =>
+        new(q.a / factor, q.b / factor, q.c / factor, q.d / factor);
+    public static Quadrilateral operator /(Quadrilateral q, Float3 factor) =>
+        new(q.a / factor, q.b / factor, q.c / factor, q.d / factor);
+
+    public static bool operator ==(Quadrilateral a, Quadrilateral b) => a.Equals(b);
+    public static bool operator !=(Quadrilateral a, Quadrilateral b) => !a.Equals(b);
+
+    // TODO: explicit conversion from polygon, check if exactly four verts, then cast.
+    public static implicit operator Quadrilateral(Fill<Float3> fill) => new(fill);
+    public static implicit operator Quadrilateral(Fill<Int3> fill) => new(fill);
+    public static implicit operator Quadrilateral(Fill<Line> fill) => new(fill);
+    public static implicit operator Quadrilateral(Fill<float> fill) => new(fill);
+    public static implicit operator Quadrilateral(Fill<int> fill) => new(fill);
+    public static implicit operator Quadrilateral((Float3 a, Float3 b, Float3 c, Float3 d) val) =>
+        new(val.a, val.b, val.c, val.d);
+}
diff --git a/Nerd_STF/Mathematics/Geometry/Triangle.cs b/Nerd_STF/Mathematics/Geometry/Triangle.cs
index e7f2228..0f0efd8 100644
--- a/Nerd_STF/Mathematics/Geometry/Triangle.cs
+++ b/Nerd_STF/Mathematics/Geometry/Triangle.cs
@@ -193,8 +193,8 @@ public class Triangle : IClosestTo<Float3>, IContains<Float3>, IContainsPartial<
               caDist = (caClosest - point).Magnitude;
 
         float min = Mathf.Min(abDist, bcDist, caDist);
-        if (abDist == min) return abClosest;
-        else if (bcDist == min) return bcClosest;
+        if (min == abDist) return abClosest;
+        else if (min == bcDist) return bcClosest;
         else return caClosest;
     }
 
@@ -207,6 +207,7 @@ public class Triangle : IClosestTo<Float3>, IContains<Float3>, IContainsPartial<
         return false;
     }
     public override int GetHashCode() => base.GetHashCode();
+    public override string ToString() => $"{nameof(Triangle)} {{ a: {a}, b: {b}, c: {c} }}";
 
     public bool Contains(Float3 point) => Contains(point, 0.05f);
     public bool Contains(Float3 point, float tolerance)
@@ -217,14 +218,24 @@ public class Triangle : IClosestTo<Float3>, IContains<Float3>, IContainsPartial<
         return Mathf.Absolute(Area - (pab.Area + pbc.Area + pca.Area)) < tolerance;
     }
     public bool Contains(Line line) => Contains(line, 0.05f);
-    public bool Contains(Line line, float tolerance) =>
-        Contains(line.a, tolerance) && Contains(line.b, tolerance);
+    public bool Contains(Line line, float tolerance, float step = Calculus.DefaultStep)
+    {
+        for (float t = 0; t <= 1; t += step)
+            if (!Contains(Float3.Lerp(line.a, line.b, t), tolerance)) return false;
+        return true;
+    }
 
     public bool ContainsPartially(Line line) => ContainsPartially(line, 0.05f);
-    public bool ContainsPartially(Line line, float tolerance) =>
-        Contains(line.a, tolerance) || Contains(line.b, tolerance);
+    public bool ContainsPartially(Line line, float tolerance, float step = Calculus.DefaultStep)
+    {
+        for (float t = 0; t <= 1; t += step)
+            if (Contains(Float3.Lerp(line.a, line.b, t), tolerance))
+                return true;
+        return false;
+    }
 
     public Float3[] GetAllVerts() => new[] { a, b, c };
+    public Line[] GetOutlines() => new[] { AB, BC, CA };
 
     public Triangle[] Subdivide()
     {
@@ -282,7 +293,7 @@ public class Triangle : IClosestTo<Float3>, IContains<Float3>, IContainsPartial<
 
     public float[] ToFloatArray() => new[] { a.x, a.y, a.z,
                                              b.x, b.y, b.z,
-                                             c.x, c.y, c.z};
+                                             c.x, c.y, c.z };
 
     public static Triangle operator +(Triangle t, Float3 offset) =>
         new(t.a + offset, t.b + offset, t.c + offset);
@@ -300,6 +311,7 @@ public class Triangle : IClosestTo<Float3>, IContains<Float3>, IContainsPartial<
     public static bool operator ==(Triangle a, Triangle b) => a.Equals(b);
     public static bool operator !=(Triangle a, Triangle b) => !a.Equals(b);
 
+    // TODO: explicit conversion from polygon, check if exactly three verts, then cast.
     public static implicit operator Triangle(Fill<Float3> fill) => new(fill);
     public static implicit operator Triangle(Fill<Int3> fill) => new(fill);
     public static implicit operator Triangle(Fill<Line> fill) => new(fill);