Shallow
 Usage
• Shallow[expr] prints as a shallow form of expr.
• Shallow[expr, depth] prints with all parts of expr below the specified depth given in skeleton form.
• Shallow[expr, {depth, length}] also gives parts whose lengths are above the specified limit in skeleton form.
• Shallow[expr, {depth, length}, form] uses skeleton form for any parts which match the pattern form.
Notes
• Omitted sequences of elements are given as Skeleton objects, which print in the form  k . • In StandardForm, the characters used for this output are \ [LeftSkeleton] and \ [RightSkeleton]. • Depth and length can be specified as Infinity. • Shallow[expr] is equivalent to Shallow[expr, {4, 10}]. • Shallow acts as a "wrapper", which affects printing, but not evaluation. • Trying to feed  k as obtained from Shallow back as input to Mathematica in StandardForm will generate an error. • New in Version 2; modified in 3.
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