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# lhs

Left hand side of equations, inequalities, relations, intervals, ranges and tables

### Use only in the MuPAD Notebook Interface.

This functionality does not run in MATLAB.

## Syntax

```lhs(f)
```

## Description

lhs(f) returns the left hand side of f.

The call lhs(f) is equivalent to the direct call op(f, 2), of the operand function op, if f is not a table.

If t is a table, the call lhs(t) returns the list of keys of the table (left hand side). Note that the i-th value in rhs(t) corresponds to the i-th key in lhs(t).

## Examples

### Example 1

We extract the left and right hand sides of various objects:

```lhs(x = sin(2)), lhs(3.14 <> PI), lhs(x + 3 < 2*y),
rhs(a <= b), rhs(m-1..n+1)```

The operands of an expression depend on its internal representation. In particular, a "greater" relation is always converted to the corresponding "less" relation:

`y > -infinity; lhs(y > -infinity)`

`y >= 4; rhs(y >= 4)`

### Example 2

We extract the left and right hand sides of the solution of the following system:

`s := solve({x + y = 1, 2*x - 3*y = 2})`

`map(op(s), lhs) =  map(op(s), rhs)`

Calls to lhs and rhs may be easier to read than the equivalent calls to the operand function op:

`map(op(s), op, 1) = map(op(s), op, 2)`

However, direct calls to op should be preferred inside procedures for higher efficiency.

`delete s:`

### Example 3

We extract the keys (left hand side) and values (right hand side) from a table:

```t := table(1=2, 4=PI, 5=5.6, 19=1/2):
l := lhs(t);```

`r := rhs(t);`

Note that the i-th value corresponds to the i-th key:

`bool(r = map(lhs(t), e->t[e]))`

`delete t,l,r:`

## Parameters

 f An equation x = y, an inequality x <> y, a relation x < y, a relation x <= y, an "is element of"-relation x in y, an interval x...y, a range x..y or a table table(x=y,...)

f

## See Also

### MuPAD Functions

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