A + b = b + a ;
a + ( b + c ) = ( a + b ) + c ;
a + ( b – c ) = a + b – c ;
a – ( b + c ) = a – b – c ;
a – ( b – c ) = a – b + c ;
a • ( b + c ) = ab + ac ;
a • ( b – c ) = ab – ac ;
( a + b ) • c = ac + bc ;
( a – b ) • c = ac – bc ;
( a + b ) : c = a : c + b : c ;
( a – b ) : c = a : c – b : c ;
a • b = b • a ;
a • ( b • c ) = ( a • b ) • c .