.model test
.inputs A0 A1 B0 B1 start c
.outputs C0 C1 C2

.subckt FA a=A0 b=A1 c=start carryout=CARRY1 sum=C0d
.subckt FA a=A1 b=B1 c=CARRY1 carryout=C2d sum=C1d

.latch C0d C0 re c 0
.latch C1d C1 re c 0
.latch C2d C2 re c 0

.end

.model FA
.inputs a b c
.outputs carryout sum
# test
.blackbox extra words
.end