Proving PTR-BCR-4

[rriyakumar]

Added in the proof for PTR-BCR-4 (on. page 23, equation 72). The following code is added:

b = dec2bin(2^5-1: -1 :0)-'0';
b1=b(:,1);b2=b(:,2);b3=b(:,3);b4=b(:,4);ba1=b(:,5);
LHS = min(reshape (b1.*b2.*b3.b4,2,[]));
RHS = min(reshape (b1 + b2 + b3 + b4 - 2ba1,2,[]));
isequal(LHS,RHS);

[ndattani]

Hi @rriyakumar, thanks so much for your work on this!
I'm a bit confused though since PTR-BCR-4 seems to have been done by @tiresias7 in Pull Request #54.

The email said:

"see if you can do the same type of verification in MATLAB for any one of the pages that have not yet been taken by a different student (see the #quadratization channel in Discord, using this version of the book)."

There's a poll on Discord where students have been selecting the page of the book that they want to work on. PTR-BCR-4 was option "B" and was taken by somebody. Luckily though, you've figured out how all this works, and it should be pretty easy for you to now do a different quadratization (that no one else selected yet).