Marie: I am not sure about the question you ask. When you ask if "other" is "invariable" I can only suggest that words can be variable in one context and invariable in other contexts. Are there other choices? Are there other alternatives. What are the other references. What other ways of articulating the idea are there. Is the correct answer other than the one offered. What other variables are involved? I am just offering some uses of "other". Hope it helps.

'Other' as an adjective is invariable, the same as all adjectives in English. In French, adjectives change according to gender and number, but in English they don't. my other sister my other sisters my other brother my other brothers You see? Singular, plural, masculine, feminine - no change. 'Other' can also be a pronoun. As a pronoun, it has a singular form (other) and a plural form (others). I don't want this book. I want the other. I don't want these books. I want the others. I hope that answers your question.

Also, I should have place question marks (?) at the end of my examples. Sorry.