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There you go Claudia brought it up to a round £20.
If you're happy to be labelled 'cis', fine. The rest of us here are not.
What is it that 'cis' women represent a subset of? Presumably, women. Now, how do you define "women"? You will need to define this subset of human beings, so it can be clear which subset of humans "cis women" represent a subsubset of and of which "transwomen" constitute another subsubset. Ditto for men and "cis men".
You can't use biological sex in your definitions, e.g. "the gender identity associated by society with [biological sex] men/women", as that will be game over: there will be biological sexes and social gender roles traditionally associated with each sex. Feminists like us accept the former and want to demolish the latter, not reinforce them.
But now you have to do precisely that, rely on social gender identity to create a category called "women". GI has to be all there is to a category: there's one group of socially created and enforced expectations, bearing on appearance, aptitude, attitudes, behaviours, etc. labelled "man" and another labelled "woman", with no explanation as to why we have these particular groups of expectations and not others—say, "likes purple, good at knitting, Capricorn, votes Tory, hates asparagus" for "man" and "fond of early Renaissance art, loves skate-boarding and WOW, vegan" for "woman". In other words, GI now has to do all the heavy lifting but with no firm ground to stand on. In reality there are good historical, economic, etc. explanations as to why the social expectations associated with each sex are the way they are.
Again, if GI is socially constructed, why do some trans people want to adjust their bodies? And even more basically: how do they know which adjustments to make? Obviously, because there really are biological sexes, and they want to resemble the outward appearance of bodies characteristic of the opposite sex.
Some transwomen are happy to keep their bodies the way they are while asserting that women can have penises, etc. (and mut.mut. for transmen). Here "women" obviously isn't biological; but it can't be traditional social GI again, as the traditional GI for women really, really doesn't include "can have a penis". So these transwomen must be constructing another GI for themselves, one that some other women do not have.
Which women, exactly? "Women who don't have penises?" When you call yourself "cis", do you really self-identify as a woman who doesn't have a penis? Obviously not. You are saying, I think, that you accept the GI society has created and labelled "woman". And off we go again: "women are those human beings who accept the GI that a given society has created out of thin air and decided to call 'woman' for no reason whatsoever".