I have a list of vectors and want to split it into elements such as

a <- list(~X1+X2, ~X2+X3)

strsplit(gsub("~", "", a[[2]])[2], "+", fixed = TRUE)[[1]]

and it gives me

"X2 "  " X3 "

I want to have separate elements without blank spaces “X2”, “X3”. How can I escape the blank spaces?