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+\documentclass{article}
+\usepackage{axiom}
+\begin{document}
+\title{\$SPAD/src/input dhtri.input}
+\author{The Axiom Team}
+\maketitle
+\begin{abstract}
+\end{abstract}
+\eject
+\tableofcontents
+\eject
+\section{License}
+<<license>>=
+--Copyright The Numerical Algorithms Group Limited 1994.
+@
+<<*>>=
+<<license>>
+-- Create Affine transformations (DH matrices) that transform
+-- a given triangle into another given triangle
+
+-- tri2tri(t1, t2) returns a DHMATRIX which transforms t1 to t2,
+-- where t1 and t2 are the vertices of two triangles in 3-space.
+tri2tri(t1: List Point DoubleFloat, t2: List Point DoubleFloat): DHMATRIX(DoubleFloat) ==
+  n1 := triangleNormal(t1)
+  n2 := triangleNormal(t2)
+  tet2tet(concat(t1, n1), concat(t2, n2))
+
+-- tet2tet(t1, t2) returns a DHMATRIX which transforms t1 to t2,
+-- where t1 and t2 are the vertices of two tetrahedrons in 3-space.
+tet2tet(t1: List Point DoubleFloat, t2: List Point DoubleFloat): DHMATRIX(DoubleFloat) ==
+  m1 := makeColumnMatrix t1
+  m2 := makeColumnMatrix t2
+  m2 * inverse(m1)
+
+-- put the vertices of a tetrahedron into matrix form
+makeColumnMatrix(t) ==
+  m := new(4,4,0)$DHMATRIX(DoubleFloat)
+  for x in t for i in 1..repeat
+    for j in 1..3 repeat
+      m(j,i) := x.j
+    m(4,i) := 1
+  m
+
+-- return a vector normal to the given triangle, whose length
+-- is the square root of the area of the triangle
+triangleNormal(t) ==
+  a := triangleArea t
+  p1 := t.2 - t.1
+  p2 := t.3 - t.2
+  c := cross(p1, p2)
+  len := length(c)
+  len = 0 => error "degenerate triangle!"
+  c := (1/len)*c
+  t.1 + sqrt(a) * c
+
+-- compute the are of a triangle using Heron's formula
+triangleArea t ==
+  a := length(t.2 - t.1)
+  b := length(t.3 - t.2)
+  c := length(t.1 - t.3)
+  s := (a+b+c)/2
+  sqrt(s*(s-a)*(s-b)*(s-c))
+@
+\eject
+\begin{thebibliography}{99}
+\bibitem{1} nothing
+\end{thebibliography}
+\end{document}