 ##  [Grushin Problem](/grushin-problem) 

  ##  [Grushin Problem](https://mathlogic.quantumdictionary.io/grushin-problem-0) 

  
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- Natural &amp; Formal Sciences -

**Mathematics &amp; Logic Dictionary**

 
Definition

A block-operator (or operator matrix) formulation that adjoins auxiliary input/output or projection operators to a non-Fredholm, degenerate, or nearly singular operator in order to obtain an extended system that is Fredholm or invertible; widely used in spectral reduction, microlocal analysis, and boundary problems.