((p -> q) (q -> p))
((C1 -> C2) (C1 -> C3) (C2 -1C3) (C3 -1C2))
y1y2((xRy1) (xRy2) (y1Ry2) (y2Ry1))
# - -
@ - -
#' - -1 -
@' - -1 -
[n] -
<n> -
[n]'-
<n>'-
& - -
| - -
~ - -
-> -
<- -
<-> -