State-dependent path conditions in specify blocks are restricted to a subset of expression types and operators (see SystemVerilog standard, Table 30-1 for the list of valid operators).
Even if some tools allow more expression types and operators, stick to the standard to keep your code portable.
module fly(input b, output c);
wire integer a;
specify
if (a === 1 + 1) (b => c) = (0,0); // Noncompliant: 'a === 1 + 1' expression is not valid in a state-dependent path condition
endspecify
endmodule