[Rafael-SOWNet]

#212 (#2183) leaves a root of x^p = v only where v is in the sector the principal power takes its values in, -p pi < arg <= p pi for 0 < p < 1. The evaluator doesn't take every power as principal, though. A negative real to a rational power whose denominator is odd and below ten is the real root to the numerator, as Number.Pow's search for a good root finds it, so (-8)^(1/3) is -2. The sector therefore dropped roots that 2.6.0 found and the evaluator confirms.

Solve("x")	2.6.0	master	now
x^(1/3) = -2	{ -8 }	{ }	{ -8 }
x^(1/5) = -2	{ -32 }	{ }	{ -32 }
x^(-1/3) = -1/2	{ -8 }	{ }	{ -8 }
x^(2/3) = 4	{ 8 }	{ 8 }	{ 8, -8 }
x^(1/3) = a	{ a ^ 3 }	… provided a = 0 or -1/3 * pi < arg(a) and arg(a) <= 1/3 * pi	the same or arg(a) = pi

• Odd numerator: the negative reals are values too, so the condition gains arg(v) = pi, and a value known to be real needs no condition, or only v ≠ 0 for a negative power.
• Even numerator: a negative base has a positive power, (-8)^(2/3) = 4, so a positive value also has the negative of its principal preimage. (-8)^(4/3) = 16 likewise.
• A denominator of ten or more, or an even one, is the principal power, as it is in the evaluator: x^(1/11) = -1 and sqrt(x) = -2 stay { }.
• One existing row pinned the regression: x^(1/3) = a with no root at a = -1. It now holds there, since (-1)^3 = -1 and (-1)^(1/3) is -1. The BREAKING-CHANGES.md entry for Support parametric solutions #212 says so.
• Found by a cross-check of 400 random equations in square and cube roots against a complex and a real Newton search, under the evaluator's convention. It also found the { } answers that A quartic that is biquadratic once depressed is solved #2314's quartic fix answers. Seven of the new cases fail on master. The suite, the trio, F#, AOT and the eight harnesses pass.

Follows #2183, for #212.

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Codecov Report

❌ Patch coverage is 90.90909% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.76%. Comparing base (3fc4022) to head (d2c865c).
⚠️ Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
...nuous/Solvers/EquationSolver/InvertNode.Classes.cs	90.90%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2313      +/-   ##
==========================================
- Coverage   86.76%   86.76%   -0.01%     
==========================================
  Files         311      311              
  Lines       68199    68216      +17     
  Branches    19821    19825       +4     
==========================================
+ Hits        59175    59187      +12     
- Misses       4881     4884       +3     
- Partials     4143     4145       +2     

Flag	Coverage Δ
cpp	37.77% <ø> (ø)
csharp	87.31% <90.90%> (-0.01%)	⬇️
fsharp	32.97% <ø> (ø)
interactive	40.72% <ø> (ø)

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Files with missing lines	Coverage Δ
...nuous/Solvers/EquationSolver/InvertNode.Classes.cs	62.13% <90.90%> (+2.13%)	⬆️

... and 1 file with indirect coverage changes

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