>Haven't heard that term used for it before . . . but perhaps it is
>because of different disciplines studying the same things using
>different jargon. There is a difference between "if - then"
>statements and "if and only if" statements.
When I was taught logic we used the term "implies" which is concise
and relatively unambiguous. "If A then B" is the same as "A implies
B", which can be written as A => B. "If and only if A then B" is the
same as saying "A =>B" AND "B =>A" (or A<=>B), because if B always
needs A then if B is true A must be true as well. Another convention
is "necessary and sufficient". If A=>B then A is sufficient for B and
B is necessary for A (think about it!). If A <=>B then A is
necessary and sufficient for B (or visa-versa).
One thought - (I'm new to this list, so apologies if this has been
discussed already) - is it necessarily the case that if a lens is
labelled MC it is definately multi-coated? What if some old single
coated lenses were erroneously labelled MC when the multi-coating
process was first introduced?
Neil.
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