# Introduction

Throughout CryptoBook, discussions are made more concise by using various mathematical symbols. For some of you, all of these will feel familiar, while for others, it will feel new and confusing. This chapter is devoted to helping new readers gain insight into the notation used.

If you're reading a page and something is new to you, come here and add the symbol, someone else who understands it can explain its meaning

# Mathematical Objects

## Special Sets

• $\mathbb{C}$: denotes the set of complex numbers

• $\mathbb{R}$: denotes the set of real numbers

• $\mathbb{Z}$: denotes the set of integers

• $\mathbb{Q}$: denotes the set of rational numbers

• $\mathbb{N}$: denotes the set of natural numbers (non-negative integers)

• $\mathbb{Z}/n\mathbb Z$: denotes the set of integers mod $n$

"""We can call each of these sets with Sage using the following commands. Comments are the result of theinput."""CC# Complex Field with 53 bits of precisionRR# Real Field with 53 bits of precisionZZ# Integer RingQQ# Rational FieldNN# Non negative integer semiringZmod(11) # or Integers(11) or IntegerModRing(11) # Ring of integers modulo 11
• We refer to unit groups by $R^\times$ or $R^*$. Example: $(\mathbb Z/n \mathbb Z)^\times$

• We refer to finite fields with $q$ elements by $\mathbb{F}_q$

• We refer to a general field by $k$

• We refer to the algebraic closure of this field by $\bar{k}$

"""Example of defining a field and then its algebraic closure"""GF(3)# Finite Field of size 3 , where GF stands for Galois Field GF(3).algebraic_closure()# Algebraic closure of Finite Field of size 3
"""If you want to find which field an element belongs to you can use the .parent() function"""​x = 7print(x.parent())# Integer Ring​y = 3.5print(y.parent())# Real Field with 53 bits of precision
"""If you want to "lift" an element from a quotient ring R/I to the ring Ruse the .lift() function"""R = ZZRI = Zmod(11)x =  RI(5)​print(x.parent())# Ring of integers modulo 11​y = x.lift()print(y.parent())# Integer Ring​print(y in R)# True

## Relation operators

• $\in$means is an element of (belongs to)

## Logical Notation

• $\forall$means for all

• $\exists$means there exists. $\exists!$ means uniquely exists

## Operators

• $Pr(A)$ means the probability of an event $A$to happen. Sometimes denoted as $Pr[A]$or as $P(A)$