3083: Not now accepts only one argument
3083_not:Changes
3083_not:changed args to arg
3083_not: Rectified a mistake of previous commit- arg.arg changed to arg.args
I hope it is correct now.
Incorrect Exception in dsolve()
added tests
added tests
Extened the named groups module to include information about

whether or not the naemd groups are nilpotent or solvable.
extended_named_groups : some corrections.
Merge pull request #1810 from meclark256/extended_named_groups

Extended the named groups module to include information about nilpotency and solvability
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Merge pull request #1783 from rishabh-git/3083_not

Issue3083: Not accepts only one argument
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Merge pull request #1803 from Manoj-Kumar-S/1996_issue

Incorrect Exception in dsolve() : First implementation
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Fixed Issue 3576
Update sympy/core/symbol.py

Indentations are corrected.
Update sympy/core/tests/test_symbol.py

Test Cases for different types of Parentheses examples have been added.
symbols allows escaping of ,; and space

Also, only one layer of surrounding parentheses are removed from
ranges, so if they are doubled, one pair will remain:

symbols('x((1:3))') -> (x(1), x(2))
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