This has one 8-bit input bus, in, and one 4-bit output bus, out. Also present is a sel input, which is used to select what appears on out. If sel is false, then out should contain the lower 4-bits of in (i.e. in[0], in[1], in[2], in[3]). If sel is true, then out should contain the upper 4-bits of in (i.e. in[4] mapped to out[0], in[5], mapped to out[1], etc.).

what are the parts

CHIP HiLoMux { IN in[8], sel; OUT out[4]; PARTS: //put your code here }

this is from nand2tetris