## STACK Documentation

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# Inequalities

The non-strict inequalities $$\geq$$ and $$\leq$$ are created as infix operators with the respective syntax

>=,  <=

Maxima allows single inequalities, such as $$x-1>y$$, and also support for inequalities connected by logical operators, e.g. $$x>1 \mbox{ and } x<=5$$.

You can test if two inequalities are the same using the algebraic equivalence test, see the comments on this below.

Chained inequalities, for example $$1\leq x \leq2\mbox{,}$$ are not permitted. They must be joined by logical connectives, e.g. "$$x>1$$ and $$x<7$$".

Support for inequalities in Maxima (and hence STACK) is currently poor. This is on our list of possible projects, and help would be welcome!

# Functions to support inequalities

### * ineqprepare(ex)

This function ensures an inequality is written in the form ex>0 or ex>=0 where ex is always simplified. This is designed for use with the algebraic equivalence answer test in mind.

### * ineqorder(ex)

This function takes an expression, applies ineqprepare(), and then orders the parts. For example,

ineqorder(x>1 and x<5);

returns

5-x > 0 and x-1 > 0

It also removes duplicate inequalities. Operating at this syntactic level will enable a relatively strict form of equivalence to be established, simply manipulating the form of the inequalities. It will respect commutativity and associativity and and and or, and will also apply not to chains of inequalities.

If the algebraic equivalence test detects inequalities, or systems of inequalities, then this function is automatically applied.

However, to establish the equivalence of x^2>1 with x>1 or x<-1 will require significantly more work. This is an interesting and open mathematical and CAS challenge!