Expression Structure
A foundational idea in Mathematica is that all expressions—whatever they may represent—ultimately have a uniform tree-like structure.
FullForm — the full functional form of an expression, without shortened syntax
TreeForm — a representation of the tree structure of small expressions
Head — the head of an expression: the
f in
Length — the number of elements in an expression
Level — parts specified by a given number of indices
Depth — the maximum number of indices to specify any part
Expression Sizes & Signatures
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