Re: Future/Modal 'will'
Ultimately it depends on one's definition of 'tense' and so, as Tdol said, there can be no 'proof'.
If one restricts the word to inflected forms of the verb, then there are clearly only two tenses, as exemplified by work/worked and bring/brought.
Those who believe this, as I do, consider such forms as the 'progressive' and 'perfect' to be 'aspects'; these forms also have present and past tenses.
The core modals, can/could, may/might, must, shall/should, will/would, are not in themselves part of the English tense system, any more than, for example, BE + going to or used to, though some of them convey ideas which are conveyed by tenses in other languages. The modal forms in bold sometimes function as the past tense of the modal form immediately preceding them, and sometimes appear to function as modal verbs in their own right - but that is a different issue.
Most modern writers on grammar accept the two-tense idea for English (and other Indo-European languages (including German), but the idea of the Will form as the future tense is so firmly entrenched in many people's minds, and still presented in many EFL course books and grammars aimed at learners, that it will probably be around for a long time yet.
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