Sindbad~EG File Manager

struct term * fsubst3(struct term *a, struct term *x, struct context *c1, struct term *b, struct context *c2, struct trail **trp);
   // substitute a for x in b, using context c,  renaming bound variables in c if necessary
struct term * fsubst5(struct term *a, struct term *x, struct context * c1, struct term *b, struct context *c2, struct trail **trp, int mask);   
   // substitute a for constant x in b, skipping terms occuring inside induction-functor symbols
int blocking_functor(int f);