[Tugindia] black board fonts

[Bhaskaracharya Pratishthana]

Hi,

I have one question about black board fonts which we use using \mathbb 
command. suppose C, the 'C' printed using mathbb is like writing double 
'C' but in actual practise when we actual write the 'C' or letter 
denoting set of Complex numbers we write it as CI where I very close to 
'C' or by C\!\!I gives some what that effect. What is the exact 
convention for Symbol denoting set of Natural number, Complex numbers?

regards,
Manjusha Joshi