146  Pascal Report  the program or are standard ("pll,'declared") entities. Pascal defines a  fixed set of operators, each of \\ hich can be regarded as describing a  mapping from  the operand typ."s  into  the result type.  The set of  operators is divided into four gn 'ups.  The  procedure  statement cau ',es the execution of the designated  procedure (see below). Assignm( lit and procedure statements are the  components, or "building block<' of  structured  statements, which  specify  sequential,  selective,  llr  repeated  execution  of  their  components. Sequential execution of statements is  specified by the  compound  statement, conditional or selective execution by the  if  and  case  statements, and repeated exe'l'ution by the  repeat, while, andjor  statements. The if statement  serve~  to make the execution of a statement  dependent on the value of a Boolean expression, and the case statement  allows the selection among many ,tatements according to the value of  an  ordinal expression.  The  for  ,tatement is  used to  execute the  component statement while each  If  a succession of ordinal values is  assigned  to  a  so-called control  variable.  The  repeat  and  while  statements are used otherwise.  In addition, Pascal provides a,  I  If  I I  statement, which indicates that  execution is to continue at anothel place in the program; that place is  marked by a  label,  which must be .lcl'lared.  Statements along with declal :11 Ions  of labels, constants, types,  variables, procedures, and functiOJ.  ,Ire  collected together into  blocks.  The  labels,  constants,  variables,  types,  procedures  and  functions  declared in a block may be referil,'d to only within that block, and  therefore  are  called  local  to  tl It'  block.  Their  identifiers  have  significance only within the progralll text that constitutes the block and  that is called the  scope  of these ick'ntifiers. Blocks are the basis for  1.  Arithmetic  operators  al'e  addition,  subtraction,  sIgn  inversion, multiplication, division, and modulus.  2.  Boolean  operators  ar,,'  negation,  union  (or),  and  conjunction (and).  3.  Set  operators are union, intersection, and set difference.  4.  Relational  operators are I;'quality, inequality, ordering, set  membership,  and  set  inclusion.  The  result  type  of  relational operators is B ,olean. 