Maths discipline altering ridiculously thick-skinned copper? (8,8)

I believe the answer is:

integral calculus

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'maths discipline altering ridiculously thick-skinned copper?' is the definition.
I can't judge whether this definition defines the answer.

'altering ridiculously thick-skinned copper?' is the wordplay.
'ridiculously' indicates anagramming the letters.
'thick skinned copper?' becomes 'calculus' (I am not sure about this - if you are sure you should believe this answer much more).
'altering' is an anagram of 'integral'.
'integral'+'calculus'='INTEGRAL CALCULUS'

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I've seen this clue in The Times.

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