// These identifiers are built in to POV-Ray, ready to use
//  #declare pi = 3.1415926535897932384626 
//  #declare e.. = 1*10^... // 3.4e4 = 34000, 2e-5 =0.00002 ; 
//  #declare E.. = 1*10^... // 3.4E4 = 34000, 2E-5 =0.00002 ; 
//  #declare true = 1 
//  #declare yes = 1 
//  #declare on = 1 
//  #declare false = 0 
//  #declare no = 0 
//  #declare off = 0 
//  #declare u = <1,0> 
//  #declare v = <0,1> 
//  #declare o = <0,0,0> 
//  #declare x = <1,0,0> 
//  #declare y = <0,1,0> 
//  #declare z = <0,0,1> 
//  #declare t = <0,0,0,1> 

// Other built in identifiers with no fixed values :
/*
version         // version (default 3.6, can be changed with #version)
image_width     // width of current render
image_height    // height of current render
input_file_name // string of the name of the input file of the scene
// values set by running an animation ini file:
clock           // current clock value in animations (0..1)
clock_delta     // clock step between frames
initial_clock   // start clock value (+KIn.n)
final_clock     // end clock value (+KFn.n)
initial_frame   // start frame number (+KFIn.n)
final_frame     // end frame number (+KFFn.n)
frame_number    // current frame number
clock_on        // 1(true) if animation
*/