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Re: [OM] SC vs MC: The Green Reflection Test

Subject: Re: [OM] SC vs MC: The Green Reflection Test
From: "Neil Bell" <neil.bell@xxxxxxxxxxx>
Date: Sat, 17 Apr 1999 12:40:11 +0000
>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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