PC' vs PC

In my writeup describing the KURM09 ISA, I frequently use the notation R' where R is a register, the PC or some variable.  This notation refers to the value of R in the next state.  So, when I say PC':=PC+2 when describing an instruction, I'm saying that the next value of the program counter is the current value plus 2.

This is different from software where the concept of state is hidden.  For example:

x = 1;
x = x+1;

in the software world results in a state where x=2.  However, the concept of state is hidden - we change state when each statement is executed.  In hardware, the state change must be explicit.  Thus, my use of R'.