changed seq x types to act the same as Int -> x
added the 'coerce' method; support for ranges of int expressions; implemented duality of mod/quant operators (e.g., some, one, none)
fixed some bugs in alloy_printer: (1) set comprehension should not break its body into multiple lines, (2) integer arithmetic operators should transate to built-in int functions
added hamiltonian predicates to the graph model