P-TAC: a parallel intermediate language

P-TAC is an intermediate-level language designed to capture the sharing of computation. It is a more suitable internal language for functional language compilers than the X-calculus or combinators, especially for compiler optimize, tions. Using P-TAC, a proof for the confluence of Id, a higher-order functional language augmented with I-structures? is given. Using the notion of observational congruence the correctness of some compiler optimizations is shown.