In this problem, let REF(x.i)DEF(x.k) denote that the linker will associate a reference to symbol x in module i to the definition of x in module k. For each example that follows, use this notation to indicate how the linker would resolve references to the symbol in each module. If there is a link-time error (rule 1), write error. If the linker arbitrarily chooses one of the definitions (rule 3), write unknown.

(1) (1.1) REF(main.1) DEF( (1.2) REF(main.2) DEF( ___.__). (2.1) REF( main.1) DEF( (2.2) REF(main.2) DEF (3) (3.1) REF(x.1) DEF( ______- ). (3.2) REF(x.2)DEF( (4.1) REF(x.1)DEF( (4.2) REF(x.2)DEF