r * s == if isint(r)
== then if isint(s) then r * s else let i,j = s in <r * i, j> fi
== else let p,q = r in if isint(s) then <p * s, q> else let i,j = s in <p * i, q * j> fi
== fi
r * s == if isint(r;tt;ff)
== then if isint(s;tt;ff) then r * s else let i,j = s in <r * i, j> fi
== else let p,q = r in if isint(s;tt;ff) then <p * s, q> else let i,j = s in <p * i, q * j> fi
== fi