MOD function returns modulus of two integer arguments. Non-integer arguments are first turned into integers by floor operation. Note that division by zero invokes DIVISION-BY-ZERO condition.

(mod -1 5) => 4                                                              
(mod 13 4) => 1                                                              
(mod -13 4) => 3                                                             
(mod 13 -4) => -3                                                            
(mod -13 -4) => -1                                                           
(mod 13.4 1) => 0.4                                                          
(mod -13.4 1) => 0.6