Brute Force Techniques I

Verilog Code

module demo(x1, x2, x3, x4, f);
    input x1, x2, x3, x4;
    output f;
    assign g = (~x1 & x2) | (x1 & ~x2);
    assign f = (g & x3) | (~g & x4);
endmodule

Waveform

Schematic