An extension 
of a group, ring, module,
field, etc., such that 
.
Proper Extension
See also
Extension Field, Extension Ring, Group Extension, Proper, Proper Subfield, Proper Submodule, Proper Subset, Proper SupersetThis entry contributed by Margherita Barile
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Barile, Margherita. "Proper Extension." From MathWorld--A Wolfram Web Resource, created by Eric W. Weisstein. https://mathworld.wolfram.com/ProperExtension.html