Function is.fvlist() returns a logical scalar with attributes
attr(,'r')
\(x\)-axis, or the \(r\)-values
attr(,'fname')
see explanation of this attributes in function fv
attr(,'.x')
spatstat.explore::fvnames(x, a = '.x') returns
attr(,'.y')
spatstat.explore::fvnames(x, a = '.y') returns