* .save can store an expression (differential voltage)
V1 p 0 SIN(0 1 1k)
V2 n 0 SIN(0 0.7 1k)
R1 p 0 1k
R2 n 0 1k
.save v(p) v(n) vdiff=par('v(p)-v(n)')
.tran 50u 1m
.end