module mux4_1(out,in0,in1,in2,in3,sel);
output out;
input in0,in1,in2,in3;
input[1:0] sel;
reg out;
always @(in0 or in1 or in2 or in3 or sel)
    case(sel)
2'b00: 	out=in0;
2'b01: 	out=in1;
2'b10: 	out=in2;
2'b11: 	out=in3;
default: out=2'bx;
    endcase
endmodule