var u: bool 

module M1:
var c1: bool
output a : { true ==> c1' = ~c1 & u' = ~u}
output b : {true ==> c1' = ~c1}
endmodule

module M2:
var c2: bool 
output b : { true ==> c2' = ~c2 & u' = ~u}
endmodule

module M3: 
var c3: bool 
output a : { true ==> c3' = ~c3 }
endmodule