wrong output with nor in brackets

[pabloaul]

#import "@preview/truthfy:0.6.0": truth-table
#let nor = math.arrow.b
#truth-table(
    $x nor y$,
    $(x nor x) nor (y nor y)$
)

will output the following table:

however I'm pretty sure the last expression should only be true for the case x = 1, y = 1