PC = PC+1; fetch     // start fetching varnum2  (fetching of varnum1 performed by Main1)
OPC = H = MBRU       // opc,h <-- varnum1
MAR = LV+H; rd       // start reading M[LV + varnum1]
H = MBRU             // h <-- varnum2
MAR = LV+H; rd       // start reading M[LV + varnum2]
H = MDR+1            // h <-- M[LV + varnum1] +1
PC = PC+1; fetch     // start fetching next opcode 
MDR = MDR+H+1; wr; goto Main1  // M[LV + varnum1] <-- M[LV + varnum1] + M[LV + varnum2] +2 and to beginning of interpreter