Introduce new context so signal end of an operation body.
Op composition working except for the second opcall PO on op;asgn;op.
Assignment context performs different ubs depending on when it is applied. Also rewrote last x~ to x so it matcches with rest of predicate.
Allow OpDef Context to stitch preCond when there are not state variables.
Flip order of substitution prints
Load subLast in instance vars even though it's useless.